太阳内部磁场的限制与锂燃烧的关系
Confinement of the Sun's interior magnetic field, with implications for lithium burning
摘要：
解释太阳辐射包层均匀旋转的最简单的内部磁场B_i是一个由深环向场稳定的轴向偶极子。只有在极冠内才能解释均匀自转。必须防止磁场向上扩散到高纬度对流区，因为高纬度对流区的较慢旋转必须与辐射内部保持解耦。本文介绍了新的分析和数值解的相关磁流体动力学方程显示，这种限制和解耦是动态可能的层流“磁约束层”在底部的速跃层。在微观扩散系数的实际值下，极上弱的层流下降流U~10^{-5}cm/s足以使B_i随高度呈指数衰减，而限制层的厚度只有百万埃的几分之一。日震观测结合基本动力学，以及关于在没有B_i的情况下将差异旋转向下传播的“陀螺泵”的理论论证，都暗示了极地速跃层中的下降流。我们的限制层解决方案是第一个考虑到所有相关的物理效应在一个自洽的数学模型。这些效应包括磁扩散、斜压性和稳定层结（热层结和成分层结）、科里奥利效应和热松弛。我们将讨论如何限制层在每个极点可能适合到一个全球性的动态图片的太阳速跃层。这张照片，反过来，提出了一个新的见解早期太阳和太阳锂耗尽。
英文摘要：
The simplest interior magnetic field B_i that can explain the observed uniform rotation of the Sun's radiative envelope is an axial dipole stabilized by a deep toroidal field. It can explain the uniform rotation only if confined in the polar caps. The field must be prevented from diffusing up into the high-latitude convection zone, whose slower rotation must remain decoupled from the radiative interior. This paper describes new analytical and numerical solutions of the relevant magnetohydrodynamic equations showing that such confinement and decoupling is dynamically possible by means of a laminar "magnetic confinement layer" at the bottom of the tachocline. With realistic values of the microscopic diffusivities, a weak laminar downwelling flow U~10^{-5}cm/s over the poles is enough to enforce exponential decay of B_i with altitude, in a confinement layer only a fraction of a megameter thick. Downwelling in the polar tachocline is implied both by helioseismic observations, combined with elementary dynamics, and by theoretical arguments about the "gyroscopic pumping" that would spread differential rotation downward in the absence of B_i. Our confinement-layer solutions are the first to take account of all the relevant physical effects in a self-consistent mathematical model. The effects include magnetic diffusion, baroclinicity and stable stratification (thermal and compositional), Coriolis effects, and thermal relaxation. We discuss how the confinement layers at each pole might fit into a global dynamical picture of the solar tachocline. That picture, in turn, suggests a new insight into the early Sun and solar lithium depletion.
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